1. Field of the Invention
The present invention relates to a fastening unit with nail anchorage intended to be introduced in a hole formed in a reception material, generally cylindrical in shape, which includes a body with a head and which has a surface portion for guiding the anchorage nail parallel to the axis of the unit, and a support leg for the nail which includes an expansion surface portion slanted in a direction with respect to the axis of the fastening unit.
The invention relates generally to a fastening unit for masonry work and, more particularly, a unit for fixing pieces to a ceiling.
If a limited crack forms in a fastening unit reception zone, it is indispensable for the unit to remain sufficiently anchored.
The fastening units known up to present do not provide a completely satisfactory solution to such a problem, not only from the technical point of view but also from the economic point of view considered simultaneously.
2. Description of the Prior Art
The European Pat. No. 0.020 919 teaches a fastening unit with nail anchorage of the above mentioned type. Besides the fact that the head of the body is in this case formed by bending the leg, the portion of the nail extending beyond the curvature, or the bending caused by the slanted expansion surface of the support leg when the nail is driven in, follows a rectilinear path along this slanted surface, which is not propitious to maintaining an adequate resilient pressure on the wall of the receiving hole when, after formation of a crack, its opening is enlarged. It is not certain that such a fastening unit will remain anchored in a crack.
The applicant already knows the American Pat. No. 4 116 105 which also describes a fastening unit with nail anchorage. This fastening unit includes a ball, slanted with respect to the axis of the unit for receiving the nail and the nail is arranged so as to bend, when it is driven in, in contact with the wall of the reception hole and then to follow the joint surface between the body of the unit and the wall of the hole.
It is true that the nail undergoes bending on coming out of the bore. But, not only does the bending angle of the nail depend only on the resistance of the receving material and that of the body of the fastening unit and, in this respect, is difficult to master, but bending of the nail is further accompanied by a deformation of its section.